Studies are ongoing to examine the interaction between human lymphocytes and human thyroid cells in tissue culture. Co-culture of these cells has been found to lead to the release, into the culture medium, of prostaglandin-like substances, that, in turn, stimulate thyroid cell cAMP generation. It is proposed to measure by radioimmunoassay various prostaglandins released into the culture medium under these conditions, and to compare these concentrations with cAMP-stimulatory bioactivity present in the medium. It is also planned to examine whether or not lymphocytic prostaglandin generation is of biological significance in the pathogenesis of Graves' disease.